The economic cultivation of phototrophic microorganisms (microalgae, cyanobacteria, purple bacteria) on an industrial scale has not yet been solved, owing to the problems of light supply, monoseptic culture conditions and scaling-up. To date, no universal standard system is available for the large-scale cultivation of phototrophic microorganisms. Of the many tens of thousands of representatives of phototrophic microorganisms, at present only a few dozen are produced in relatively large amounts, and these are generally produced in open systems, which are not free from contamination. To date, the culture conditions of phototrophic microorganisms, in pilot-scale production in closed reactors, cannot be kept constant for an extended period, as the phototrophic microorganisms that form in a culture phase are deposited on the reactor walls, which leads to fluctuations in the amount of light supplied to the culture medium and to variable mixing of the culture medium. Algal deposits are often caused by stress conditions (e.g. through shearing) during cultivation, the causes of which can be uncontrolled growth conditions (e.g. light, temperature in open-pond and closed reactors) of the microorganisms or induction of the production of valuable substances by the phototrophic organisms (e.g. astaxanthin, beta-carotene).
A closed photobioreactor for cultivating algae is known from WO 2008/055190 A2. The materials used are glass or plastics such as polyethylene, PET, polycarbonate. Detaching microorganisms from the surfaces of bioreactors by means of ultrasound is described in DE 10 2005 025 118 A1. In US 2003/0073231 A1 and US 2007/0048848 A1, deposits are removed by mechanical means, for example brushing. These are relatively laborious methods, which are not arbitrarily scalable. In DE 44 16 069 A1 it is recommended to provide light-conducting fibers used for illuminating bioreactors with a smooth surface. US 2008/0311649 A1 proposes increasing the flow rate of the algae-containing medium in tubular bioreactors, to prevent deposition of the algae. This has the disadvantage that the culture parameters with respect to flow rate can no longer be set independently.
In WO 2008/132196 A1, crosslinkable polyorganosiloxane-polyoxyalkylene copolymers are recommended as antifouling coating in the marine area, in particular for coating metal or concrete, for example ships' hulls, buoys, drilling rigs. Later in this publication there is discussion of GB 1307001, which describes the coating of hulls with silicone resins to prevent fouling, and of U.S. Pat. No. 3,702,778, which describes the coating of hulls with silicone rubber. It can be seen from WO 2008/132196 A1 that in both cases effective prevention of fouling is only achieved at relatively high flow rate on the hull. To prevent fouling of underwater structures, it is recommended in WO 01/94487 A2 to apply glass-like interpenetrating polymer networks based on silanol-terminated silicones and alkoxy-functionalized siloxanes, together with two separable agents, at least one of which grafts onto the glass matrix. Silicone coatings are described in this document as being unstable in a marine environment, with the disadvantage that the coating must be renewed frequently. In Biofouling, 2007, 23(1), 55-62 it is recommended to apply silicone-based antifouling paint films on hulls in particular patterns. Paints that only contain silicones are described as not inherently antifouling. In WO 2008/145719 A1, transparent LED plastic moldings are used for illuminating photoreactors. For this, it is preferable to use moldings in which LEDs are embedded in a silicone molded article.